Geant4 Low Energy Polarized Processes

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Geant4 Low Energy Polarized Processes

• Gerardo Depaola
• Francesco Longo

National University of Córdoba (Argentina)
University of Ferrara and INFN (Italia)
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Talk Outline

• Compton Effect
• Angular Distribution for Scattered gamma.
• Vector Polarization distribution.
• Pair Production
• Azimuthal distribution.
• Effect of polarization
• Asymmetric ratio.

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COMPTON SCATTERING
The Klein Nishina cross section
Where, h?0 energy of incident photon. h?
energy of the scattered photon. ? angle between
the two polarization vector
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Angles in the Compton Effect

• ? Polar angle
• ? Azimuthal angle
• ? Polarization vector

x
x
f
hn
?
A
hn0
q
z
a
O
C
y
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Angular distribution Scattered Radiation
compose of two components e and e respect
to AOC plane
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Summing over the two direction the
cross section can be write as

• Sample Methods implemented in G4LowEnergyPolarized
  Compton class
• Integrating over ?
• Sample ?
• Theta - Energy Relation Energy
• Sample of ? from P(?) a (b c cos2 ?)
  distribution

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Results

• Class inserted in next G4 release
• To be compared with Experimental results
• Scattered Polarization

? distribution obtained with the class
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Scattered Photon Polarization
? is obtain from cos ? cos ? N and ? is sample
from Klein Nishina cross section
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Test of the distribution a) low energy b) high
energy
The distribution function is
where and ? h? /
h?0.
Low energy h?o ltlt mc2 gt h? ? h?o gt
? 1 gt a 0 the distribution
reduces to the Thompson distribution
gt the probability that the two
polarization vectors are perpendicular
is zero.
High energy small ? gt h? ? h?o
gt equal to low energy
high ? it is possible to demonstrate that
b/(ab) -gt0, so in this case the distribution
tend to be isotropic.
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Results

• Scalar product between the two polarization
  vectors for three different energies.
• Upper histograms Low polar angle ?
• Lower histograms High polar angle ?

100 keV
10 MeV
1 MeV
These distributions are in agreement with the
limits obtained previously.
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PAIR PRODUCTION

• Cross Section

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Angles occurring in the pair production
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Azimuthal Distribution of a Pair Created by 100
MeV Photon.
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Effects of polarization
Asymmetric Ratio nº of pairs contains in
plane parallel to the vector polarization to nº
of pairs perpendicular
Asymmetric ratio for pair production
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Asymmetric ratio for Compton scattering
Polar aperture
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Polar aperture
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In progress

• Test the Compton class with experimental data.
• Include the binding effect in the Compton class.
• Build the class for pair production.
• Develop a class for
• 1) Rayleig scattering
• 2) Photoelectric effects